Polycarbonate resin composition useful in optical applications

ABSTRACT

A polycarbonate resin composition comprising a blended mixture of 
     (A) a polycarbonate resin having a viscosity average molecular weight of from about 13,000 to about 18,000, 
     (B) 0.0001 to less than 0.02% by weight, based on the weight of the resin (A), of an organic phosphine, and 
     (C) 0 to 0.5% by weight, based on the weight of the resin (A), of a partial ester of a monobasic fatty acid having 10 to 22 carbon atoms with a polyhydric alcohol having 2 to 10 carbon atoms, 
     the amount of the partial ester (C) being 0.01 to 0.5% by weight when the amount of the organic phosphine (B) is not less than 0.005% by weight, and said composition containing less than 0.004%, based on the weight of the resin (A), of chlorine.

This invention relates to a polycarbonate resin composition having a lowchlorine content, and specifically, to a polycarbonate resin compositionhaving various excellent properties such as excellent flowability,thermal stability, moldability and hydrolysis resistance and pinholeformation resistance on a thin coated layer on the surface of a moldedarticle prepared from the resin composition. The polycarbonate resincomposition of this invention is useful in many applications, especiallyin optical applications.

More specifically, this invention relates to a polycarbonate resincomposition comprising a blended mixture of

(A) a polycarbonate resin having a viscosity average molecular weight offrom about 13,000 to about 18,000,

(B) 0.0001 to less than 0.02% by weight, based on the weight of theresin (A), of an organic phosphine, and

(C) 0 to 0.5% by weight, based on the weight of the resin (A), of apartial ester of a monobasic fatty acid having 10 to 22 carbon atomswith a polyhydric alcohol having 2 to 10 carbon atoms,

the amount of the partial ester (C) being 0.01 to 0.5% by weight whenthe amount of the organic phosphine (B) is not less than 0.005% byweight, and said composition containing less than 0.004%, based on theweight of the resin (A), of chlorine.

Polycarbonate resins have been used in a wide range of applications, andrecently attracted attention as resins which give substrates forinformation recording articles such as digital signal recording discsand optical video discs, optical articles such as lenses, prisms andFresnel lenses and excellent molded articles for use in other opticalapplications.

In such optical uses, one important property required of thepolycarbonate resin is that a molded article of the polycarbonate resinhas a reduced optical distortion (retardation). Generally, such a resinarticle is essentially required to have a birefringence of not more than100 nm. To obtain such low-birefringence molded articles, it is theusual practice to use a polycarbonate resin having a viscosity averagemolecular weight of not more than about 20,000. Since the moldingtemperature for such a polycarbonate resin reaches about 300 to about400° C., it is desired to use a polycarbonate resin composition havinghigh thermal stability and excellent mold releasability.

In optical applications, for example as a substrate for informationrecording devices, it is frequently the practice to provide a thincoated layer of a metal or a metal compound or a thin coated layercontaining a dye on the surface of the substrate. Furthermore, in usingthe polycarbonate resin as a lens, a thin coated layer of a metal, ametal compound, an organosiloxane-type paint or a melamine-type paint isfrequently applied to the lens surface for prevention of scratching, orfor antihaze and antiglare purposes. In such optical applications, it isdesired to use a polycarbonate resin composition having excellenthydrolysis resistance, excellent resistance to pinhole formation on thethin coated layer, and therefore a satisfactory life or durability.

Generally, polycarbonate resins contain at least 40 ppm, for example 40to 100 ppm, as chlorine, of chlorine-containing compounds used in theirproduction such as methylene chloride as a solvent or compounds havingan unreacted chloroformate group. These chlorinecontaining compoundsdecompose to generate acidic substances when the resins are molded athigh temperatures of, for example, 300° C. or higher. The acidicsubstances will corrode molds. When a thin film of a metal or a metalliccompound, a thin film containing a dye, or another type of thin film isprovided on the surfaces of the molded products, these acidic substanceswill also cause degeneration of the thin films or the dye.

It is desired therefore to use a polycarbonate resin of a low chlorinecontent which is highly purified to remove the chlorine-containingcompounds that cause these troubles. Thorough removal ofchlorine-containing compounds, however, is restricted both in operationand cost. Even with a polycarbonate resin of a low chlorine content ofless than 0.004% by weight, it has previously been impossible to avoidburn marks or coloration in molding at a temperature of, for example,350° C. or higher. Addition of a phosphite ester most widely used as aheat stabilizer for conventional general polycarbonates can obviate burnmarks or coloration, but when the resulting molded product is exposed toa high-temperature high-humidity atmosphere for an extended period oftime, the average molecular weight of the polycarbonate decreases.Furthermore, when the aforesaid thin film is to be applied to thesurface of the molded product as in optical applications, the phosphiteester heat stabilizer inevitably affects the thin films adversely.

Accordingly, in using a low chlorine polycarbonate resin, particularlyin optical applications, a molding composition of the resin is desiredto have excellent thermal stability, moldability, and pinhole formationresistance on a thin coated layer on the surface of a molded articleprepared from the resin composition.

It is extremely difficult, however, to provide a polycarbonate resincomposition having excellent properties that meet the aforesaid variousrequirements, and it has been desired to develop such a composition.

Some proposals have previously been made for the use of an organicphosphine corresponding to the component (B) of the composition of thisinvention as a heat stabilizer for polycarbonate resins.

For example, Japanese Patent Publication No. 22088/1972 (published onJune 21, 1972) discloses heat-resistant resin composition prepared byadding an organic phosphine compound represented by the followingformula ##STR1## wherein R₁, R₂ and R₃ each represent hydrogen, alkyl,cycloalkyl, alkenyl, phenyl or aralkyl, which may be sustituted byalkyl, or alkoxy or amino, or to a polycarbonate resin or polyphenyleneoxide resin in order to increase the thermal stability of syntheticresins having high processing temperatures including polycarbonateresins.

This patent document states that the amount of the organic phosphineused is preferably 0.01 to 10%, especially 0.1 to 2%, and in Example 1which is the sole example of incorporating the phosphine into apolycarbonate resin, the phosphine is used in an amount of about 0.5% byweight. The patent document, however, does not at all refer to thecomponent (C) of the composition of this invention, and naturallyneither describes nor suggests that when the amount of the phosphine isin the range of not less than 0.005% by weight which range includes thelower limit 0.01% described in this patent document, the phosphine(component B) must be used in combination with the component (C) in thisinvention. This patent document totally fails to suggest the aforesaidtechnical problems and the technical idea and means for solving theseproblems which are described hereinabove with regard to the low chlorinepolycarbonate resin or composition specified in the present invention.The composition of this patent document does not satisfy thequantitative relationship between the components (B) and (C) set forthhereinabove and in the claims. As will be shown later in ComparativeExample 4, when the component (B) alone is used in an amount of 0.5% byweight, a number of pinholes occur upon wet heat treatment in analuminum film vacuum deposited on a molded circular plate obtained fromthe resulting composition. Furthermore, as shown in Comparative Example3, when the component (B) alone is used in an amount of 0.01% by weight,pinholes, although small in number, occur in an aluminum film vacuumdeposited on a molded circular plate obtained from the resultingcomposition.

As another proposal, British Patent No. 1,350,338 published on Apr. 18,1974 (corresponding to West German OLS No. 2,206,720 and JapaneseLaid-Open Patent Publication No. 90350/1973) describes a thermallystable aromatic polycarbonate composition comprising an aromaticpolycarbonate resin having in admixture therewith from 0.005 to 0.5weight percent, based on the weight of the polycarbonate, of a phosphineof the formula PR₃ where each R is an alkyl, aryl or alkaryl radical.This patent describes that the amount of the phosphine used is in therange of 0.005 to 0.5 weight percent, but the amounts of it usedspecifically in working examples are in the range of 0.02 to 0.1%. Thispatent neither refers to the component (C) of the composition of thisinvention. Naturally, therefore, the patent does not describe norsuggest that in the quantitative range of not less than 0.005% by weightwhich range includes the amounts in the examples of the patent and theaforesaid lower limit 0.005% by weight, the components (B) and (C)should be used in combination. In addition, this patent totally fails tosuggest the aforesaid technical problems and the technical idea andmeans for solving these problems which are described hereinabove withregard to the low chlorine polycarbonate resin or composition specifiedin the present invention. Furthermore, it should be pointed out thatComparative Examples 3 and 4 given hereinbelow show that when thecomponent (B) is used in an amount of not less than 0.005% by weight, asatisfactory improvement cannot be achieved unless it is used incombination with the component (C).

As still another proposal, Japanese Laid-Open Patent Publication No.90254/1985 (laid-open on May 21, 1985) discloses a process for theproduction of polycarbonate shaped articles of a thermoplasticpolycarbonate composition by a devolatilizing injection-molding processor a devolatilizing extrusion process, wherein the composition containsa phosphane of the general formula (R)₂ PR¹ in which R is anunsubstituted or substituted C₆ -C₁₄ aryl radical and R¹ is anunsubstituted or substituted C₁ -C₁₈ alkyl radical. This patent documentstates that the amount of the phosphane used is 0.01 to 1% by weight,preferably 0.02 to 0.5% by weight, especially 0.05 to 0.2% by weight,based on the total weight of the polycarbonate and phosphane. Thispatent document totally fails to refer to the component (C) of thecomposition of this invention. Naturally, therefore, it neitherdescribes nor suggests that when the amount of the phosphane is in therange of not less than 0.005% by weight which range includes the lowerlimit 0.01% described in this patent document, the component (B) shouldbe used in combination with the component (C). In addition, this patentdocument totally fails to suggest the aforesaid technical problems andthe technical idea and means for solving these problems which aredescribed hereinabove with regard to the low chlorine polycarbonateresin or composition specified in the present invention. Furthermore,the composition of this patent document does not satisfy thequantitative relationship between the components (B) and (C) set forthhereinabove and in the claims.

Other proposals have been known which utilize an ester or partial esterthat can overlap the component (C) of the composition of this inventionas a lubricant for improving the releasability of a molded article of apolycarbonate resin from a mold.

Japanese Patent Publication No. 41092/1972 (published on Oct. 17, 1972),for example, discloses a polycarbonate resin composition comprising apolycarbonate resin and as a lubricant for improving the releasabilityof a molded product from a mold, 0.05 to 5% by weight, preferably 0.1 to0.5% by weight, of an ester or partial ester of a monobasic saturatedaliphatic carboxylic acid having 12 to 30 carbon atoms with a monohydricsaturated aliphatic alcohol or a polyhydric alcohol. The lubricant inthis patent document includes partial esters which can overlap component(C) of the composition of the present invention. This patent document,however, totally fails to describe or suggest the organic phosphine (B)which is an essential component in the composition of this invention.Naturally, therefore, it neither describes nor sugggest the quantitativerelationship beteeen the components (B) and (C) specified hereinaboveand in the claims nor the combination of (A), (B) and (C) in thecomposition of this invention. This patent document fails to describethe utilization of the polycarbonate resin composition in opticalapplications, the technical problems in such applications and an idea ofsolving such problems. Furthermore, this patent document illustratesonly the use of polycarbonate resins having a molecular weight exceedingabout 20,000, for example 24,000 and 25,000.

Japanese Laid-Open Patent Publication No. 81245/1985 (laid open on May9, 1985) discloses a polycarbonate resin composition comprising apolycarbonate resin having a viscosity average molecular weight of15,000 to 35,000 and containing 15 to 150 ppm, calculated as chlorineatoms, of a chlorine compound such as methylene chloride and 0.001 to0.5% by weight, preferably 0.03 to 0.1% by weight, of a partial ester,preferably a monoester, of a monobasic saturated aliphatic carboxylicacid having preferably 10 to 24, more preferably 12 to 20, carbon atoms,with a polyhydric alcohol in order to prevent the corrosion of a moldwhich adversely affects the appearance of a molded article prepared fromit, the releasability of the molded article from the mold, thedimensional accuracy of the molded article, and the life of the mold,etc. The partial ester in this patent document can overlap the component(C) in the composition of this invention. However, this patent documenttotally fails to refer to the essential organic phosphine component (B)of the composition of this invention. Naturally, therefore, it neitherdescribes nor suggests the quantitative relationship between thecomponents (B) and (C) specified hereinabove and in the claims nor thecombination of (A), (B) and (C) in the composition of this invention.Furthermore, it does not touch upon the utilization of the compositionin optical applications, the technical problems in such utility, and anidea of solving these problems.

The present inventor has made investigations in order to provide apolycarbonate resin composition which generates a chlorine-containingacidic substance to such an extent as to give rise to no substantialproblem, and even in a high-temperature high-humidity atmosphere, doesnot adversely affect a thin film of a metal or a metallic compound oranother thin film to be adhered to the surface of a molded article ofthe composition.

It has consequently been found that the components (B) and (C)satisfying the following combination parameters exhibit superb improvingeffects in overcoming the various troubles mentioned above, particularlythose in optical applications, which occur even when one selects a lowchlorine polycarbonate resin having a chlorine content of less than0.004% by weight and a viscosity average molecular weight of from about13,000 to about 18,000.

(B) 0.0001 to less than 0.02% by weight, based on the weight of theresin (A), of an organic phosphine, and

(C) 0 to 0.5% by weight, based on the weight of the resin (A), of apartial ester of a monobasic fatty acid having 10 to 22 carbon atomswith a polyhydric alcohol having 2 to 10 carbon atoms.

In the above components (B) and (C), when the amount of the organicphosphine (B) is not less than 0.005% by weight, the amount of thepartial ester (C) is 0.01 to 0.5% by weight.

It is an object of this invention therefore to provide a polycarbonateresin composition having various improved properties which is especiallyuseful in optical applications.

The above and other objects of this invention along with its advantageswill become apparent from the following description.

The polycarbonate resin (A) in the composition of this invention and themethod of its production are known. Commercially available polycarbonateresins can also be used in this invention.

The polycarbonate resin component (A) may be produced by techniquesknown per se by reacting dihydric phenols with carbonate-precursors suchas phosgene and diphenyl carbonate. Examples of the dihydric phenols arehydroquinone, dihydroxydiphenyl, bis(hydroxyphenyl)alkanes,bis(hydroxyphenyl)cycloalkanes, bis(hydroxyphenyl)ethers,bis(hydroxyphenyl)ketones, bis(hydroxyphenyl)sulfides,bis(hydroxyphenyl)sulfones and brominated or lower alkylated productsthereof. A polycarbonate resin derived from a bis(hydroxyphenyl)alkaneand a carbonate precursor is preferred. The bis(hydroxyphenyl)alkanemay, for example, be at least one member selected from the groupconsisting of 2,2-bis(4-hydroxyphenyl)-propane (bisphenol A),1,1-bis(4-hydroxyphenyl)ethane and2,2-bis(4-hydroxyphenyl)hexafluoropropane. The dihydric phenols may beused singly or in combination. Polycarbonate resins obtained bycopolymerizing a small amount of an aromatic dicarboxylic acid furtheras a comonomer, and polycarbonate resins having a branched structure canalso be used. The polycarbonates may be used singly or in combination.

In the present invention, the polycarbonate resin (A) has a viscosityaverage molecular weight (M) of from about 13,000 to about 18,000. Ifthe molecular weight (M) is lower than the lower limit specified, thestrength of a molded article from the polycarbonate resin isunsatisfactory for practical applications. If it is higher than thespecified upper limit, molding strains tend to occur during molding, andthe molded articles become unsuitable for optical applications becausethey undergo degradation in regard to optical distortion, color, andtransparency. Accordingly, in the present invention, the polycarbonateresin (A) used should have viscosity average molecular weight (M) offrom about 13,000 to about 18,000.

The viscosity average molecular weight M of the polycarbonate resin (A)used in this invention is obtained by measuring the specific viscosityη_(sp) of a solution of 0.7 g (=C) of the resin in 100 ml of methylenechloride at 20° C. by an Ostwald's viscometer, calculating the intrinsicviscosity [η]of the resin in accordance with the equation η_(sp)/C=[η]+0.45 [η]² C, and substituting the resulting intrinsic viscosity[η] for [η] in the following equation (1).

    [η]=1.23×10.sup.-4 M.sup.-0.83                   ( 1)

Polycarbonate resins contain methylene chloride, a chloroformate of adihydric phenol, or an oligomer or polymer having a terminalchloroformate group, and the overall content of thesechlorine-containing compounds is expressed by the content of chlorine.Advantageously, the polycarbonate resin used in this invention has achlorine content of less than 0.004% by weight, preferably less than0.003% by weight, more preferably less than 0.002% by weight. If,however, the chlorine content of the polycarbonate can be reduced toless than 0.004% by weight during preparation of the composition of thisinvention, the starting polycarbonate may have a higher chlorinecontent.

The polycarbonate resin composition of this invention contains theorganic phosphine (B) in an amount of 0.0001 to less than 0.02% byweight, preferably 0.0005 to less than 0.01% by weight, based on theweight of the polycarbonate resin (A).

If the amount of the component (B) is 0.02% by weight or more, its heatstabilizing effect can be fully observed during molding of the resultingcomposition. However, when an aluminum film is vacuum-deposited on partof the surface of a molded article prepared from the resultingcomposition and the molded article is exposed for an extended period oftime to a high-temperature high-humidity atmosphere, pinholes may occurin the aluminum film, and the aluminum film loses gloss or undergoesdegradation. Hence, such an excessive amount is not suitable for thepurposes of this invention. On the other hand, it has been ascertainedthat even if the organic phosphine (B) is used alone in an amount ofless than 0.005% by weight, its heat stabilizing effect during moldingis fully achieved and pinhole formation and degeneration hardly occur ina thin coated layer on the surface of a molded article prepared from thecomposition. However, if the amount of the component (B) is less than0.0001% by weight, the heat-stabilizing effect is difficult to achieve.

When the amount of the organic phosphine (B) is in a range in which itcan be used alone, namely less than 0.005% by weight, it is preferred tochoose the resin (A) or the method of preparing the composition so thatthe final resin composition has a chlorine content of less than 0.003%by weight, preferably less than 0.002% by weight. Of course, even inthis case, the partial ester (C) may be used in combination in an amountof up to 0.5% by weight, preferably up to 0.1% by weight, for example,0.01 to 0.5% by weight, preferably 0.01 to 0.1% by weight. In the caseof using the components (B) and (C) in combination, no particularconsideration is necessary to the selection of the chlorine content ofthe resin (A) so long as the final resin composition has a chlorinecontent of less than 0.004% by weight.

When the amount of the organic phosphine (B) is not less than 0.005% byweight, preferably more than 0.0045% by weight to less than 0.02% byweight, the partial ester (C) must be used in combination in an amountof 0.01 to 0.5% by weight, preferably 0.01 to 0.1% by weight. If thepartial ester (C) is not jointly used in this case, pinholes, althoughsmall in number, occur upon wet heat treatment in an aluminum filmvacuum-deposited on a molded circular plate of the composition (seeComparative Example 3). Furthermore, if in this embodiment of conjointuse, the amount of the partial ester (C) is too small outside theabove-specified range, fine spot-like degeneration (frosting) occursupon wet heat treatment on an aluminum film vacuum-deposited on a moldedcircular plate of the composition. If it is too large beyond thespecified range, silver streaks will be formed, or discoloration willoccur, during the molding of a circular plate.

Examples of the organic phosphine (B) used in this invention aresecondary or tertiary phosphines represented by the following formula##STR2## wherein R¹, R² and R³, independently from each other, representa C₁ -C₂₀ alkyl, C₃ -C₆ cycloalkyl or C₂ -C₆ alkenyl group which mayhave a substituent such as hydroxy, acetoxy, lower alkylcarboxy, phenyl,or lower alkoxyphenyl, or a phenyl or naphthyl group which may have asubstituent such as hydroxy or C₁ -C₁₀ alkyl, and one of R¹, R² and R³may represent a hydrogen atom.

Specific examples of the organic phosphine (B) include

triethylphosphine,

triisopropylphosphine,

tri-n-butylphosphine,

tricyclohexylphosphine,

allyldiphenylphosphine,

triphenylphosphine,

diphenylphosphine,

tri-2,4-dimethylphenylphosphine,

tri-2,4,6-trimethylphenylphosphine,

tri-o-tolylphosphine,

tri-o-anisylphosphine,

diphenylbutylphosphine,

diphenyl-octadecylphosphine,

tris-(p-nonylphenyl)-phosphine,

tris-naphthylphosphine,

diphenyl-(hydroxymethyl)-phosphine,

diphenyl-acetoxymethylphosphine,

diphenyl-(beta-ethylcarboxyethyl)phosphine,

diphenyl-benzylphosphine,

diphenyl-(p-hydroxyphenyl)-phosphine,

diphenyl-1,4-dihydroxyphenyl-2-phosphine, and

phenyl-naphthyl-benzylphosphine.

The partial fatty acid ester (C) used in the composition of thisinvention is a partial ester of a monobasic fatty acid having 10 to 22carbon atoms with a polyhydric alcohol having 2 to 10 carbon atoms. Thepartial ester can be produced by esterifying the monobasic fatty acidwith the polyhydric alcohol by techniques known per se, and is alsoavailable commercially. Such commercially available partial esters canalso be used in this invention. The partial esters may be used singly orin combination, and are also available in such forms on the market.

Examples of the partial fatty acid ester (C) are partial esters formedbetween at least one monobasic fatty acid having 10 to 22 carbon atomsselected from the group consisting of myristic acid, palmitic acid,stearic acid, oleic acid and fatty acids of hardened fish oils and atleast one polyhydric alcohol having 2 to 10 carbon atoms selected fromthe group consisting of ethylene glycol, glycerin and pentaerythritol.Preferred among these partial esters are those formed between glyceroland at least one fatty acid having 18 to 22 carbon atoms such as stearicacid, oleic acid and fatty acids (e.g., C₁₈ -C₂₂) of hardened fish oils.Glyceryl monostearate is most preferred.

The polycarbonate resin composition of this invention may containadditives in addition to the components (A), (B) and (C). Examples ofthe additives are 0.01 to 0.5% by weight, based on the weight of thepolycarbonate resin (A), of a mold releasing agent other than compoundsfalling within the component (C) of the composition of this invention,such as paraffins, montan wax, stearyl palmitate, palmityl stearate,di-2-ethylhexyl adipate, beeswax, and silicone oils, and 0.1 to 0.7% byweight, based on the weight of the polycarbonate resin (A), of anultraviolet absorber such as 2-hydroxy-4-n-octoxybenzophenone,2-(2'-hydroxy-5'-methylphenyl)benzotriazole,2-(2'-hydroxy-3'-t-butyl-5'-methylphenyl) -5-chloro-benzotriazole,2-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol.

The composition of this invention can be easily prepared by mixing theessential components (A) and (B), or (A), (B) and (C), and if required,the other additives to form a blended mixture.

The mixing may be carried out by any known methods, and the sequence ofmixing the components is optional. For example, a powder or pellets ofthe polycarbonate resin (A) and the organic phosphine (B), with orwithout the partial ester (C), and as required, the other additives maysimply be mixed by using a tumbler, a V-type blender, a supermixer, etc.Alternatively, the composition of this invention may be easily preparedby mixing a solution of the polycarbonate resin (A) with the organicphosphine (B), with or without the partial ester (C) and further theother additives, and then removing the solvent. It can also be preparedby continuously introducing a powder or pellets of the polycarbonateresin (A) and the organic phosphine (B) with or without the partialester (C) and the other additives into an extruder. When a mixing methodsuch as melt-extrusion is employed, it is anticipated that the organicphosphine will be changed to another phosphorus compound. It should beunderstood that this case also falls within the scope of this invention.

The resulting composition of this invention should have a chlorinecontent of less than 0.004% by weight, preferably less than 0.003% byweight, more preferably less than 0.002% by weight, based on the weightof the polycarbonate resin (A). When the starting polycarbonate resin(A) has a chlorine content of less than 0.004% by weight, thecomposition may be prepared by mechanically mixing all the requiredcomponents. But if the polycarbonate resin (A) has a chlorine content of0.004% by weight or more, it is recommended to melt-mix all the requiredcomponents in a vent-equipped extruder. The chlorine content of theresin composition can be determined by hydrolyzing the sample with anaqueous solution of sodium hydroxide and then quantitatively analyzingthe hydrolyzed sample by the Volhard method.

The composition of this invention in the form of a melt-molded articlefor optical applications may be produced by injection molding,compression molding or injection-compression molding. Especiallypreferred conditions for injection molding are a resin temperature of320° to 380° C. and a mold temperature of 70° to 120° C.

The composition of this invention in the form of a molded article foroptical applications is very transparent with a light transmittance ofabout 90% and has a very small optical distortion typified by itsbirefringence. Furthermore, even when various thin films as describedhereinabove are applied to the molded article, they do not undergodegeneration. Accordingly, it has excellent utility as a substrate forvarious information recording discs, and various lenses, prisms andFresnel lenses.

The following Examples and Comparative Examples illustrate the presentinvention. The birefringence and transmittance of a molded circularplate and the appearance of a molded circular plate having avacuum-deposited coating in these examples were measured and determinedby the following methods.

Mesurement of birefringence

Resin pellets were injection-molded into a circular plate having athickness of 1.2 mm and a diameter of 120 mm by a 3-ounce injectionmolding machine (Neomat 150/75 type, made by Sumitomo Heavy MachineryIndustry Co., Ltd.) at a resin temperature of 350° C. and a moldtemperature of 110° C. The birefringence of the plate was measured at aposition 30 mm away from the center of the plate toward its peripheralportion by using a polarization analysis device (Ellipsometer) made byMizoshiri Kogaku Kogyosho Co., Ltd., and expressed in nm.

Measurement of transmittance

The transmittance of the molded circular plate above was measured by aHitachi self-recording spectrophotometer (model U-3400) at a wavelengthin the range of 500 to 1000 nm, and expressed in %.

Evaluation of a molded article having a vacuum-deposited coating

The molded circular plate mentioned above was put into a bell jar of avacuum depositing device, and aluminum was vapor-deposited only on onesurface of the plate at 10⁻⁵ torr. A polyurethane resin was coated onthe plate, and the plate was left to stand for 72 hours in aconstant-temperature constant-humidity machine in an atmosphere kept ata relative humidity of 95% and a temperature of 85° C. Then, the numberof pinholes formed in the aluminum film was counted. Pinholes areundesirable since they prevent accurate recording of information.

The polycarbonate resins used in the following examples were synthesizedfrom 2,2-bis(4-hydroxyphenyl)propane and phosgene.

EXAMPLES 1-6, 8 AND 11

In each run, a polycarbonate resin powder having an average molecularweight of 14,900 was mixed with the organic phosphine (B) and thepartial ester (C) in the proportions indicated in Table 1. The mixturewas extruded at 260° C. by using a 30 mm vent-equipped extruder. Theextruded thread was cut by a cutter to obtain pellets. The viscosityaverage molecular weight and chlorine content of the pellets were asshown in Table 1.

The pellets were injection-molded into a circular plate having athickness of 1.2 mm and a diameter of 120 mm by a 3-ounce injectionmolding machine at a resin temperature of 350° C. and a mold temperatureof 110° C.

An aluminum film was vacuum-deposited on the molded circular plate, anda polyurethane resin was coated on the plate. The coated plate wassubjected to wet heat treatment, and a change in appearance wasevaluated by the number of pinholes that occurred. The results are shownin Table 1.

EXAMPLE 7

Example 2 was repeated except that a polycarbonate resin powder havingan average molecular weight of 17,100 was used instead of thepolycarbonate resin powder used in Example 2. The results are shown inTable 1.

EXAMPLES 8-9

Example 7 was repeated except that the polycarbonate resin powder havingan average molecular weight of 17,100 was mixed with the organicphosphine (B) and the partial ester (C) in the proportions indicated inTable 1. The results are shown in Table 1.

COMPARATIVE EXAMPLE 1

Example 1 was repeated except that the organic phosphine (B) and thepartial ester (C) were not added. The results are shown in Table 1. Themolded circular plate assumed a yellow color and was found to beunsuitable for optical applications.

COMPARATIVE EXAMPLES 2, 3, 5 AND 8

Example 1 or 7 was repeated except that the amounts of the organicphosphine (B) and the partial ester (C) were outside the ranges definedby the quantitative relationship set forth in the claims. The resultsare shown in Table 1. The molded circular plates showed satisfactoryproperties, but upon wet heat treatment, some pinholes occurred in thevacuum-deposited aluminum film.

COMPARATIVE EXAMPLES 4 AND 6

Example 1 was repeated except that the partial ester (C) was not added,and the amount of the organic phosphine (B) exceeded the range specifiedin the claims. The results are shown in Table 1. The molded circularplates were satisfactory, but upon wet heat-treatment, many pinholesoccurred in the aluminum film.

COMPARATIVE EXAMPLE 7

Example 2 was repeated except that the vent of the extruder was notoperated. The results are shown in Table 1. The molded circular plateslightly lacked transparency, and upon wet heat-treatment, a number ofpinholes occurred in the aluminum film.

COMPARATIVE EXAMPLE 9

Example 2 was repeated except that triphenyl phosphite (organicphosphite) was used instead of the organic phosphine (B). The resultsare shown in Table 1. The molded circular plate showed satisfactoryproperties, but upon wet heat-treatment, pinholes occurred in thealuminum film.

                                      TABLE 1                                     __________________________________________________________________________           (A) Poly-                               Number of pinholes                    carbonate                               of the circular                Example                                                                              resin                Resin composition                                                                        Circular plate                                                                        vacuum deposited               (Ex.) or                                                                             Viscosity                                                                           (B) Organic                                                                            (C) Partial                                                                         Viscosity  Trans-                                                                            Bire-                                                                             coating                        Comparative                                                                          average                                                                             phosphine                                                                              ester**                                                                             average                                                                             Chlorine                                                                           mit-                                                                              fring-                                                                            Before                                                                             After                     Example                                                                              molecular Amounts                                                                            Amounts                                                                             molecular                                                                           content                                                                            tance                                                                             ence                                                                              treat-                                                                             treat-                    (CEx.) weight                                                                              Name*                                                                             (wt. %)                                                                            (wt. %)                                                                             weight                                                                              (wt. %)                                                                            (%) (nm)                                                                              ment ment                      __________________________________________________________________________    Ex. 1  14,900                                                                              a   0.0020                                                                             --    14,800                                                                              0.0014                                                                             90  10  0    0                         Ex. 2  "     a   0.0045                                                                             --    "     0.0013                                                                             91   8  0    0                         CEx. 1 "     --  --   --    "     "    (colored                                                                              --   --                                                               yellow)                                Ex. 3  "     a   0.0060                                                                             0.05  "     "    90  12  0    0                         CEx. 2 "     a   0.0060                                                                             --    "     "    90  15  0    11                        Ex. 4  "     a   0.0100                                                                             0.10  "     "    90  20  0    0                         CEx. 3 "     a   0.0100                                                                             --    "     "    90  21  0    15                        CEx. 4 "     a   0.5000                                                                             --    "     "    91  23  0    33                        Ex. 5  "     a   0.0080                                                                             0.08  "     0.0015                                                                             91  15  0    0                         CEx. 5 "     a   0.0080                                                                             --    "     "    91  17  0    14                        Ex. 6  "     a   0.0045                                                                             --    "     0.0016                                                                             91  10  0    0                         CEx. 6 14,900                                                                              a   0.0500                                                                             --    14,800                                                                              0.0016                                                                             90  15  0    19                        CEx. 7 "     a   0.0045                                                                             --    "     0.0130                                                                             87  36  0    45                        Ex. 7  17,100                                                                              a   0.0045                                                                             --    17,000                                                                              0.0017                                                                             90  17  0    0                         Ex. 8  14,900                                                                              b   0.0040                                                                             --    14,800                                                                              0.0016                                                                             91   9  0    0                         Ex. 9  17,100                                                                              b   0.0040                                                                             --    17,000                                                                              0.0015                                                                             90  20  0    0                         Ex. 10 "     b   0.0060                                                                             0.05  "     "    90  18  0    0                         CEx. 8 "     b   0.0060                                                                             --    "     "    90  19  0    12                        Ex. 11 14,900                                                                              b   0.0045                                                                             --    14,800                                                                              0.0014                                                                             90  13  0    0                         CEx. 9 "     c   0.0045                                                                             --    "     "    90  11  0    22                        __________________________________________________________________________     *a: triphenyl phosphine                                                       b: diphenyl1,4-dihydroxyphenyl-2-phosphine                                    c: triphenyl phosphite                                                        **glyceryl monostearate                                                  

What is claimed is:
 1. A polycarbonate resin composition comprising ablended mixture of(A) a polycarbonate resin having a viscosity averagemolecular weight of from about 13,000 to about 18,000, (B) 0.0001 toless than 0.02% by weight, based on the weight of the resin (A), of anorganic phosphine, and (C) 0 to 0.5% by weight, based on the weight ofthe resin (A), of a partial ester of a monobasic fatty acid having 10 to22 carbon atoms with a polyhydric alcohol having 2 to 10 carbonatoms,the amount of the partial ester (C) being 0.01 to 0.5% by weightwhen the amount of the organic phosphine (B) is not less than 0.005% byweight, and said composition containing less than 0.004%, based on theweight of the resin (A), of chlorine.
 2. The composition of claim 1wherein the polycarbonate resin (A) is a polycarbonate resin derivedfrom a bis(hydroxyphenyl)alkane and a carbonate precursor.
 3. Thecomposition of claim 2 wherein the bis(hydroxyphenyl)alkane is at leastone member selected from the group consisting of2,2-bis(4-hydroxyphenyl)propane, 1,1-bis(4-hydroxyphenyl)ethane and2,2-bis(4-hydroxyphenyl)hexafluoropropane.
 4. The composition of claim 2wherein the carbonate precursor is at least one member selected from thegroup consisting of phosgene and diphenyl carbonate.
 5. The compositionof claim 1 wherein the organic phosphine (B) is a secondary or tertiaryphosphine represented by the following formula ##STR3## wherein R¹, R²and R³, independently from each other, represent a C₁ -C₂₀ alkyl, C₃ -C₆cycloalkyl or C₂ -C₆ alkenyl group which may have a substituent such ashydroxy, acetoxy, lower alkylcarboxy, phenyl, or lower alkoxyphenyl, ora phenyl or naphthyl group which may have a substituent such as hydroxyor C₁ -C₁₀ alkyl, and one of R¹, R² and R³ may represent a hydrogenatom.
 6. The composition of claim 1 wherein the partial ester (C) is apartial ester derived from at least one monobasic fatty acid having 10to 22 carbon atoms selected from the group consisting of myristic acid,palmitic acid, stearic acid, oleic acid and fatty acids of hardened fishoils and at least one polyhydric alcohol having 2 to 10 carbon atomsselected from the group consisting of ethylene glycol, glycerol andpentaerythritol.
 7. The composition of claim 1 which is in the form of amolded article for optical applications.
 8. Use of the composition ofclaim 1 in a molded article for optical applications.